border-1px($color)
  position relative
  &:after
    display block
    position absolute
    left 0
    bottom 0
    width: 100%
    border-top: 1px solid $color
    content " "

bg-none
   &:after
     none
bg-imge($url)
     background-image:url($url+"@2x.png")
     @media (-webkit-min-device-pixel-ratio:3),(min-device-pixel-ratio:3)
       background-image url($url+"@3x.png")
